1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
<h1 id="firstHeading" class="firstHeading">Variadic functions</h1> <p>Variadic functions are functions (e.g. <code><a href="io/fprintf" title="c/io/fprintf">printf</a></code>) which take a variable number of arguments.</p>
<p>The declaration of a variadic function uses an ellipsis as the last parameter, e.g. <code><span class="kw4">int</span> <a href="http://en.cppreference.com/w/c/io/fprintf"><span class="kw851">printf</span></a><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> format, ...<span class="br0">)</span><span class="sy4">;</span></code>. See <a href="language/variadic" title="c/language/variadic">variadic arguments</a> for additional detail on the syntax and automatic argument conversions.</p>
<p>Accessing the variadic arguments from the function body uses the following library facilities:</p>
<table class="t-dsc-begin"> <tr> <td colspan="2"> <h5 id="Macros"> Macros </h5> </td>
</tr> <tr class="t-dsc-header"> <th colspan="2"> Defined in header <code><stdarg.h></code> </th>
</tr> <tr class="t-dsc"> <td> <div><a href="variadic/va_start" title="c/variadic/va start"> <span class="t-lines"><span>va_start</span></span></a></div> </td> <td> enables access to variadic function arguments <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="variadic/va_arg" title="c/variadic/va arg"> <span class="t-lines"><span>va_arg</span></span></a></div> </td> <td> accesses the next variadic function argument <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="variadic/va_copy" title="c/variadic/va copy"> <span class="t-lines"><span>va_copy</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> makes a copy of the variadic function arguments <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="variadic/va_end" title="c/variadic/va end"> <span class="t-lines"><span>va_end</span></span></a></div> </td> <td> ends traversal of the variadic function arguments <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr> <td colspan="2"> <h5 id="Type"> Type </h5> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="variadic/va_list" title="c/variadic/va list"> <span class="t-lines"><span>va_list</span></span></a></div> </td> <td> holds the information needed by va_start, va_arg, va_end, and va_copy <br> <span class="t-mark">(typedef)</span> </td>
</tr> </table> <h3 id="Example"> Example</h3> <div class="t-example">
<p>Print values of different types.</p>
<div class="c source-c"><pre data-language="c">#include <stdio.h>
#include <stdarg.h>
void simple_printf(const char* fmt, ...)
{
va_list args;
va_start(args, fmt);
while (*fmt != '\0') {
if (*fmt == 'd') {
int i = va_arg(args, int);
printf("%d\n", i);
} else if (*fmt == 'c') {
// A 'char' variable will be promoted to 'int'
// A character literal in C is already 'int' by itself
int c = va_arg(args, int);
printf("%c\n", c);
} else if (*fmt == 'f') {
double d = va_arg(args, double);
printf("%f\n", d);
}
++fmt;
}
va_end(args);
}
int main(void)
{
simple_printf("dcff", 3, 'a', 1.999, 42.5);
}</pre></div> <p>Output:</p>
<div class="text source-text"><pre data-language="c">3
a
1.999000
42.50000</pre></div> </div> <h3 id="References"> References</h3> <ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 7.16 Variable arguments <stdarg.h> (p: 269-272) </li></ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul><li> 7.15 Variable arguments <stdarg.h> (p: 249-252) </li></ul>
<li> C89/C90 standard (ISO/IEC 9899:1990): </li>
<ul><li> 4.8 VARIABLE ARGUMENTS <stdarg.h> </li></ul>
</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/utility/variadic" title="cpp/utility/variadic">C++ documentation</a></span> for <span class=""><span>Variadic functions</span></span> </td>
</tr> </table> <div class="_attribution">
<p class="_attribution-p">
© cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br>
<a href="https://en.cppreference.com/w/c/variadic" class="_attribution-link">https://en.cppreference.com/w/c/variadic</a>
</p>
</div>
|
